Electron discharge device



Dec. 15, 1936. I ,G. JoBsT ET AL I I 2,064,346

v ELECTRON DISCHARGE DEVICE Filed June 25, 1954.

INVENTOR GUNTHER JOBST FRANZ SAMMER.

A ORNEY Patented Bil 15, 1936;

STATES the PATENT ores 2,064,346 ELECTRON DISCHARGE DEVICE Application June 23, 1934, Serial No. 732,035

In Germany June 27, 1933 2 Claims. (01. 250-275) a The present invention relates to an electrode system for electron discharge tubes, particularly to an improved electrode system in which the outer electrode is constructed to facilitate the radiation of heat from the cathode but to prevent escape of electrons past the electrode. Electrode systems are shown in the prior art in which the electrode, which normally acts as an anode or plate and which is maintained at 'a high positive potential, is of the apertured type. This type is chosen for thermal reasons in order that more efficient heat transfer from the interior of the mount may be insured. Heat is generated by the hot cathode, and also as a result of the losses in the anode or plate, or the other electrodes operated at a positive potential. If heat transfer were prevented by making the anode or plate of a solid material, such as sheet metal, an inadmissibly high tempera- 20 ture would be attained inside the mount in the space around the electrodes and cause thermionic emission from cold electrodes, such as the grids, from which emission is not desired. In order to prevent this undesired emission from tak- 25 ing place, the anode is frequently made of mesh or gauze material. With this construction there is a possibility of electrons getting thru the openings in the anode and reaching the space between the anode and the glass wall where they 30 are likely to cause disturbances.

The nature of these disturbances is largely determined by the electrical condition of the inner wall of the glass bulb and of the insulators serving to support the electrode system. The

35 wall of the bulb and the insulators may be charged to a positive potential by leakage currents starting at the anode seal. This condition is very likely to arise if the plate potential is connected before the cathode has attained its full electron emission, and this is particularly true in the operation of tubes in the standard receiver sets operated directly from the supply lines. If the surfaces of the insulating parts are bombarded by electrons straying away from 45 the discharge path or penetrating thru the apertured anode at a rate of speed corresponding to the potential of the surface, these surfaces will give rise to secondary electron emission. The emitting surfaces will then act in a way simi- 50 lar to electrodes, and inasmuch as they are in a capacitive coupling relationship with the control grid, they will occasion changes in damp-ing and capacity in the grid circuit. However, even when the glass wall has no positive charge, and 55 when secondary electron emission (1 6 .0 81 6 trouble, an apertured anode is likely to cause trouble or disturbing effects. The electrons passing thru the anode are retarded in their motion as they approach the'glas's wall, and finally reverse their line of'travel. As a result a space- 5 charge is built up in the space between the anode and the glass wall, and the existence and character of the space charge is subject to a great many electrical influences inside and outside the tube. It will be evident that such a 10 tube is considerably more sensitive to external disturbances than in the case where the discharge is confined to the space inside the electrode system. Another disturbing feature is that space-charges of thesort described are frequent- 1y very unstable, and have a tendency toward abrupt changes, which become uncomfortably manifest in the loudspeaker in the form of crackling or frying noises. Under certain conditions, these space-charges may also cause vibratory actions resembling Kurz-Barkhausen oscillations.

The object of the present invention isto prevent the disturbances described above by providing a novel construction forthe outer electrode,

which will facilitate heat transfer from the space within the electrode mount but which will eirectively prevent escape of electrons from the discharge path, so that secondary emission of electrons from the glass wall and insulating supporting members will be prevented and so that a space-charge will not be built up between the glass wall and the anode.

It is desirable to also provide means which will prevent the electrons from escaping from the discharge path at the ends of the electrode system and from thus entering into the space between the glass wall and the electrode system. For this purpose, the electrode system may be closed at the ends of the mount by cover plates or end shields made of insulation or by negatively biased metallic plates or shields.

The novel features which we believe to be characteristic of our invention are set forth with particularity in the appended claims, but the invention itself will best be understood by reference to the following description taken in connection with the accompanying drawing in which Figure 1 is a transverse cross sectional view of an electron discharge device having an electrode system embodying our invention; Figure 2 is a transverse cross sectional view of an electron discharge device provided with a modification of the electrode system shown in Figure 1; and Figure 3 is a longitudinal section of a modification of the electrode system shown in Figure 1.

Referring to Figure 1 the electrode system mounted in the envelope B comprises a cathode K, the control grid G, the apertured anode or plate A, and a protective sheath or screen S surrounding the anode. This screen is made from a kind of material which is permeable to heat rays, or will freely permit the passage of. heat thru the material, but will not permit the passage of electrons. Mica may be used for this sheath. It is desirable to dispose this protective sheath or screen in close proximity to the outside of the plate in order to preclude all chances ofelectrons. accumulating between the anode and the electron screen. It would also be possible to make the anode A by spraying a metal, for example, in the form of a grid, upon the protective sheath or screen S which is not conducting for electricity. The material for the screen should bemade substantially free from secondary electron emission,

for example by de-activating it by means dis- 'to the cathode and electrically connected. These sheet-metal plates are positioned at a certain angle of inclination i with reference to surfaces t tangential to an imaginary plate cylinder 2. These sheets or strips overlap in the fashion of shutters so that the cathode will be completely covered or masked from the outside so that it will not be visible from the outside of the mount. As a result, the electrons are blocked in their travel from the cathode to the anode from going into the space outside the anode. The strips of sheetmetal are mirrored or polished at least. on the inside and so positioned that. the heat rays will be reflected towards the outside as indicated by the broken line 10.

In the modification shown in Figure 3 the electrode system comprises a cathode K having an electron-emissive layer E, a control grid G, and an apertured or foraminous anode A mounted inside a protective screen S, which is permeable to heat and which is arranged as in Figure 1.

The two ends of the electrode assembly are covered by the cover members or shields S, and these latter may be disk shaped and consist of an insulating material that is free from secondary electron emission and may be employed to assist in the supporting of the electrodes, or they may be metallic plates at negative or. at. cathode potential in which case there is no contact between the shields and the electrodes in the mount. It is preferable to extend the anode A and the screen S beyond the cover plates or shields S in order to prevent electrons from escaping thru whatever spaces or cracks there may be between the shields and anode intothe space outside of the anode.

While we have. indicated the preferred embodiments of our invention of which we are now aware and have also indicated only one specific application for which our invention may be employed,v it will be apparent that our invention is by no means limited to the exact forms illustrated or the use indicated, but that many variations may be made in the particular structure used and the purpose for which it is employed Without departing from the scope of our invention as set forth in the appended claims.

What we claim as new is- 1. An electron discharge tube having an envelope containing a thermionic cathode, a grid around said cathode and an apertured outer electrode surrounding the cathode and grid and a sheath around said outer electrode, said sheath being permeable to heat rays but an insulator for electricity.

2. An electron discharge tube having an envelope containing a thermionic cathode, a grid around said cathode and. an apertured outer electrode surrounding the cathode and grid and a sheath of insulating material around said outer electrode in close proximity thereto, said sheath being permeable to heat and substantially free from secondary electron. emission.

FRANZ SAMMER. GI'TNTHER JoBsT. 

